1. Description of the Prior Art
The invention relates to a device and a method for the rejection of interference in a signal.
It can be applied notably in the context of telecommunications where the payload signal received may be subjected to the addition of powerful jamming or interference phenomena which, however, are completely different from thermal noise. This parasitic signal is mostly “narrowband noise” compared with the payload signal, i.e., it can be locally likened to a pure carrier of almost-constant amplitude with a “slowly” variable frequency.
The invention is applicable to the rejection of any signal that can be likened to a narrowband signal.
2. Description of the Prior Art
In the prior art, there are essentially three techniques used to reject the interference referred to in the present invention.
The first technique, known as the Frequency Selective Limiter or FSL technique consists of the processing of a signal in blocks which generally overlap one another. For each block, the transform of the signal is computed and is then compared with the theoretical value that it should have. In the next processing operation, for each complex value of said transform, the amplitude (and not the phase) is modified in such a way that the effects of the interference are as small as possible. Such a modification may consist in giving the theoretical amplitude to all the points, setting those points whose amplitude is “too high” at zero or using any other appropriate processing operation. An inverse Fourier transform reconstitutes the signal which, in principle, is rid of the interference.
The second technique is that of “adaptive filtering” which consists of the continuous adjustment of the coefficients of a filter known as a “predictive” filter to minimize the mean square error between the signal that it predicts and the preceding signal samples. The inverse filter of the predictor is then used to filter the signal so as rid it of the majority of the interference or jamming phenomena that affect it
Finally, the third technique known as the “rejection filter” technique consists in estimating the long-term frequency spectrum of the interference phenomena, computing a filter that attenuates the signal received in the frequency band or frequency bands and applying the filter before demodulation.